In various applications using sealing materials for semiconductor LSIs and the like, various resin compounds prepared by mixing an inorganic filler with a resin have been used and proposed.
Nowadays, inorganic fillers having a variety of compositions, average particle diameters, powder properties, and electrical properties are generally used for mixing with resins.
If a filler is added to a resin having high fluidity, an increased amount of the filler added typically decreases the fluidity of the resin compound after finishing adding of the filler, even the particle diameter of the filler or the viscosity of the resin influences. In contrast, if the particle diameter of the filler is large, an increase in the amount of the filler added does not always decrease fluidity. So, a plurality of fillers including a filler mainly for achievement of performance and a filler for control of the fluidity of the resin compound are added in many case.
Examples of the filler mainly for achievement of performance include various powders of metals and/or metal oxides. Examples of the filler for fluidity control include silica powders and carbon black.
In some cases, fillers including silica powders having same composition and different particle diameters having a wide particle size distribution may be used to achieve control of the fluidity of a resin compound. Further, the controlled fluidity and improvement of the filler content may be achieved by the filler such as an irregularly-shaped ferrite powder by making the particle size distribution wide.
A filler is selected depending on the intended application. If a magnetic filler is used for an electromagnetic wave absorption, it is difficult to achieve both a high filler content and a high volume resistivity because control of the various powder properties (such as the average particle diameter, particle size distribution, and shape) of the magnetic filler and adjustment of electrical properties is necessary.
Application using many ferrite powders as magnetic fillers have been proposed. For example, Patent Document 1 (Japanese Patent Laid-Open No. 5-335121) discloses a magnetic sealing material made of a resin containing a ferrite powder surface-treated with a silane coupling agent. It is stated that the magnetic sealing material provides an increased strength and good mold releasability.
Patent Document 2 (Japanese Patent Laid-Open No. 2005-139050) discloses a spherical magnetic ferrite powder having a volume specific resistivity of 5×107 Ωm (5×109 Ωcm) or more at 120° C. and a volume specific resistivity of 3×109 Ωm (3×1011 Ωcm) or more at 25° C. In addition, Patent Document 2 further discloses a resin compound for semiconductor sealing that contains the magnetic ferrite powder which is used together with a silica particle.
Patent Document 2 states that the magnetic ferrite powder disclosed has electromagnetic wave shielding ability and electrical insulating properties, and further, the resin compound for semiconductor sealing which contains the magnetic ferrite powder is highly reliable.
Patent Document 3 (Japanese Patent Laid-Open No. 2005-347449) discloses a soft magnetic powder having a frequency particle size distribution in which a maximum value A exists in the range from 10 μm to 50 μm and a minimum value B exists in the range from 0.5 μm to 10 μm (exclusive of 10 μm); and an organic material prepared by blending the soft magnetic powder with a resin or rubber. Patent Document 3 states that a molded product excellent in electromagnetic wave absorption and heat radiation should be manufactured.
However, the magnetic powders disclosed in Patent Documents 1 to 3 are not the magnetic powder that are good in filling ability if used as a filler, are not excellent in handling properties, and are not high in resistivity prepared even if various powder properties (such as the average particle diameter, particle size distribution, and shape) and electrical properties are adjusted.
Patent Document 4 (Japanese National Publication of International Application NO. 2007/108437) discloses a silica powder at least characterized in that the maximum frequency value for the mode peak 1 present in the particle size range from 1 to 4 μm and a maximum frequency value for the mode peak 2 present in the particle size range from 15 to 55 μm observed in the volume frequency particle size distribution determined by a laser diffraction-scattering method. Wherein, the maximum frequency value for the mode peak 2 is greater than that for the mode peak 1; the mode peak 2 has a shoulder; and the content of particles having particle size range of 15 to 55 μm is greater than the particles having particle size range of 1 to 4 μm. It is also stated that the composition including the silica powder blended with at least either one of rubber or resin is used as a semiconductor-sealing material.
Patent Document 4 states that a sealing material filled with a high content of silica powder which has good moldability, and is less in burr generation should be manufactured. However, Patent Document 4 relates to a silica powder used as a filler for fluidity control and does not relate to a ferrite powder used as a filler for achievement of performance.